By this rule, Scandy has two years to figure it out. I'd say he's shown enough upside to still bet on an NHL career. I'd also say kids who jump in and are great young like Doughty and Karlsson are more exceptions than the rule.

Everyone dreams of a Doughty and Karlsson on draft day, and everyone's memory seems to just be 2-3 drafts deep. But most defensemen are (as you say) longer term projects than that. Just to give some examples from players I randomly picked off the top of my head:

Tom Gilbert - First NHL season (ignoring his 12 game stint) at 24
Hal Gill - First NHL season at 22
Zdeno Chara - Had a partial season at 21-22, first 60+ NHL game season at 22-23
Brian Rafalski - First NHL season at 26
Marek Zidlicky - First NHL season at 26
Duncan Keith - First NHL season at 22
Matt Carle - First NHL season at 22
Dan Boyle - First 60+ NHL game season at 24

To put that in perspective, Scandella's first 60+ game season was at age 21. I'm sure all sorts of people would love to have a player like Keith on our team, but how would you have felt about him in 2006 after he went 9-12-21 with a -11 in 81 games? I don't expect Scandella to be as good as Duncan Keith, but he's not meaningfully behind him statistically or timing-wise in his development.